Optical waveguide

ABSTRACT

Disclosed herein is an optical waveguide comprising a core layer to be an optical transmission region, an upper clad layer and a lower clad layer covering the core layer, in which the core layer, the upper clad layer and the lower clad layer are formed from resin materials, characterized in that a microlens made of a material having a higher refractive index than that of a material constituting said core layer is disposed in the vicinity of an end face of said core layer.

The priority Japanese Patent Application Number 2004-78014 which thispatent application is based is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical waveguide.

2. Description of the Related Art

In recent years, under circumstances where the trend of Internet towardbroadband moves forward, it is necessary to reduce the cost of devicesfor optical communication by a large amount for widespread use of accesssuch as FTTH. Optical transmitter and receiver modules to convert lightto electrical signals are used in terminals of equipment for opticalcommunication as a device for optical communication. In order to bringthis optical transmitter and receiver module down in size and cost,there is proposed a method in which an optical waveguide, being a partwithin the module, is formed from an organic polymeric material (NobuoMiyadera, “Polymeric materials for an optical waveguide”, OpticalAlliance, 1999, no. 2, p. 13).

For example, a lower clad layer is formed on a substrate, and on thislower clad layer, an optical transmission layer consisting of an organicpolymeric material is formed. In this optical transmission layer, apattern is formed and an unnecessary portion is eliminated by reactiveion etching (RIE) and ultraviolet (UV) irradiation usingphotolithography. On the optical transmission layer thus formed, anupper clad layer is formed. In many case, the lower clad layer and theupper clad layer are also formed from an organic polymeric material.

SUMMARY OF THE INVENTION

It is a first object of the present invention to provide an opticalwaveguide which can be easily fabricated and has a function of a lens atan end portion.

It is a second object of the present invention to provide an opticalwaveguide of which optical transmission characteristics can be easilymeasured externally.

It is a third object of the present invention to provide an opticalwaveguide which is easy to be aligned in being connected to anotherpart.

It is a fourth object of the present invention to provide an opticalwaveguide in which a thickness of a residual layer formed between anupper clad layer and a lower clad layer around a core layer can beeasily controlled.

An optical waveguide according to a first aspect of the presentinvention is an optical waveguide comprising a core layer to be anoptical transmission region, an upper clad layer covering the core layerand a lower clad layer, in which the core layer, the upper clad layerand the lower clad layer are formed from resin materials, and ischaracterized in that a microlens consisting of a material having ahigher refractive index than that of a material constituting the corelayer is located in the vicinity of an end face of the core layer.

In accordance with the first aspect of the present invention, it ispossible to locate the microlens in the vicinity of an end face in thecore layer to form the core layer and simultaneously to fix themicrolens at a predetermined position. Therefore, the optical waveguidewhich can be easily fabricated and has a function of a lens can be made.

In the first aspect, it is preferred that the microlens has asubstantially spherical or cylindrical shape. When the core layer isformed in a groove formed in the lower clad layer or the upper cladlayer, the microlens can be positioned by contacting the microlens withat least two inner wall surfaces in the groove. Therefore, it ispossible to form the core layer and to secure the microlens in a stateof thus positioning the microlens.

A configuration of the groove constituting the core layer is notparticularly limited and includes, for example, a rectangularconfiguration, a “V” configuration and a pentagonal configuration. Whenthe groove has a rectangular configuration, the microlens can bepositioned by a side wall and a bottom of the groove by using the groovehaving the width approximately equivalent to a diameter of themicrolens. And, when the groove is composed of inclined surfaces, bottomportions of which intersect, such as a “V” configuration or a pentagonalconfiguration, a microlens having a spherical shape or a cylindricalshape can be positioned by meeting with these two inclined surfaces.

A microlens used in the first aspect is not particularly limited as longas it can be located in the core layer and has transparency for awaveguided light, and includes for example, substances formed from resinor glass. For example, perfectly spherical polystyrene particles whichare used as a standard sample of a particle size distribution analyzeror a particle counter is given are given.

An optical waveguide according to a second aspect of the presentinvention is an optical waveguide comprising a core layer to be anoptical transmission region, an upper clad layer covering the core layerand a lower clad layer, in which the core layer, the upper clad layerand the lower clad layer are formed from resin materials, and ischaracterized in that the optical waveguide is constructed in such a waythat a light scattering region, in which bubbles or particles arecontained, is formed in part of the core layer and a waveguided light inthe core layer is scattered by the light scattering region and part ofthe scattered light can be extracted out of the optical waveguide.

In accordance with the second aspect of the present invention, since itis possible to scatter the waveguided light in the core layer with thelight scattering region and to extract part of the scattered light outof the optical waveguide, the extracted light can be monitored by aphotodetector such as a photodiode. Therefore, optical transmissioncharacteristics in the optical waveguide can be easily measuredexternally.

A diameter of the bubble or particle in the second aspect is preferablyat least a wavelength of the waveguided light in order to scatter thewaveguided light efficiently.

Bubbles to be contained in the core layer can be formed by injecting amaterial for forming a core layer containing bubbles into a groove ofthe core layer. The material for forming a core layer containing bubblescan be prepared by bubbling nitrogen gas into a region of the materialfor forming a core layer through a porous filter.

Particles contained in the light scattering region is not particularlylimited as long as it can scatter light and include, for example, glassparticles, resin particles and metal particles. A diameter of particleis preferably at least a wavelength of the waveguided light as describedabove, and for example, it is preferably within a range of 2 to 4 μm inthe case of a single mode waveguide and preferably within a range of 2to 10 μm in the case of a multi mode waveguide.

Also, A diameter of the above-mentioned bubble is preferably within sucha range.

An optical waveguide according to a third aspect of the presentinvention is an optical waveguide comprising a core layer to be anoptical transmission region, an upper clad layer covering the core layerand a lower clad layer, in which the core layer, the upper clad layerand the lower clad layer are formed from resin materials, and ischaracterized in that a light scattering region, in which bubbles orparticles are contained, is formed in part of the upper clad layerand/or the lower clad layer.

In the third aspect, the light scattering region is formed in part ofthe upper clad layer and/or the lower clad layer. By forming the lightscattering region in the upper clad layer or the lower clad layer, partof a waveguided light transmitting through the core layer can beextracted externally. Therefore, by detecting this extracted light,optical transmission characteristics in the optical waveguide can beeasily measured externally as with the second aspect.

Further, by forming the light scattering region in the upper clad layeror the lower clad layer, this light scattering region can be easilyidentified externally. By forming this light scattering region in aposition to facilitate identifying an end portion of the core layer,alignment of the core layer becomes easy in connecting the opticalwaveguide to another part.

In the third aspect, bubbles to be contained in the light scatteringregion can be formed by injecting a material for forming a clad layercontaining bubbles into a predetermined position for the lightscattering region to be formed. The material for forming a clad layercontaining bubbles can be prepared as with the material for forming acore layer containing bubbles in the second aspect.

And, as a particle in the third aspect, a substance similar to aparticle in the second aspect can be employed.

As a method of concentrating bubbles in a material for forming a cladlayer at specified location, there is given, for example, a method inwhich bubbles are concentrated around a projection by covering a cladlayer with a mold having a projection when curing the upper clad layeror lower clad layer.

An optical waveguide according to a fourth aspect of the presentinvention is an optical waveguide comprising a core layer to be anoptical transmission region, an upper clad layer covering the core layerand a lower clad layer, in which the core layer, the upper clad layerand the lower clad layer are formed from resin materials, and ischaracterized in that spacers are located between the upper clad layerand the lower clad layer around the core layer.

In accordance with the fourth aspect, by locating spacers between theupper clad layer and the lower clad layer around the core layer, athickness of a residual layer formed between the upper clad layer andthe lower clad layer around the core layer can be easily controlled.That is, by adjusting the dimension and the location of the spacers, thethickness of the residual layer can be easily controlled.

In the fourth aspect, in both regions straddling the core layer, spacersmay be located in only one region. Particularly in a curved portion ofthe optical waveguide, the leakage of the waveguided light to theoutside of the curved portion can be suppressed by locating the spacersin only an inside region of the curved portion to relatively thin thethickness of the residual layer outside the curved portion and torelatively thicken the thickness of the residual layer inside the curvedportion in order to suppress leakage of the waveguided light since thewaveguided light is apt to leak outside the a curved portion.

As a spacer used in the fourth aspect, there can be used, for example,spacers which are inserted between opposed substrates in a liquidcrystal display. As such a spacer, a plastic spacer, a glass spacer andthe like are known and as it shape, a particle form spacer, a rod formspacer and the like are known. And, when a spacer having a small size isused, a standard sample exemplified as a microlens in the first aspectcan be used.

In the first to fourth aspects of the present invention, the core layer,the upper clad layer and the lower clad layer are formed from resin basematerials. As the resin base material, it is preferred to employ anorganic-inorganic composite material. By employing the organic-inorganiccomposite material, it is possible to form an optical waveguide whichhas excellent optical transmission characteristics and high heatresistance, chemical resistance and mechanical strength.

The organic-inorganic composite material can be formed, for example,from an organic polymer and metal alkoxide. And, the organic-inorganiccomposite material may be formed from at least one kind of metalalkoxide. In this case, it is preferably formed from at least two kindsof metal alkoxides.

In the above-mentioned organic-inorganic composite material, arefractive index of an organic-inorganic composite material finallyformed can be adjusted by appropriately adjusting the combination of theorganic polymer and the metal alkoxide or the combination of at leasttwo kinds of metal alkoxides.

As the metal alkoxide, metal alkoxide having a polymerizable group whichis polymerized by light (ultraviolet light) or heat may be employed. Inthis case, it is preferred to use the metal alkoxide having apolymerizable group which is polymerized by light or heat and metalalkoxide not having the polymerizable group in combination. As theabove-mentioned polymerizable group, there are given a methacryloxygroup, an acryloxy group, a vinyl group, a styryl group, and the like.When the clad layer or the core layer to be cured by ultravioletirradiation is formed from an organic-inorganic composite materialcontaining metal alkoxide, it is preferred to contain metal alkoxidehaving a polymerizable group to be polymerized by light (ultravioletlight) as metal alkoxide.

When the metal alkoxide having a polymerizable group is used, it ispreferred that a polymerizable group of metal alkoxide has beenpolymerized by light or heat.

As the metal alkoxide, there are given alkoxides of Si, Ti, Zr, Al, Sn,Zn, Nb and the like. Particularly, alkoxide of Si, Ti, or Zr ispreferably used. Accordingly, alkoxysilane, titanium alkoxide, zirconiumalkoxide and niobium alkoxide are preferably used, and particularly,alkoxysilane is preferably used.

As the alkoxysilane, there are given tetraethoxysilane,tetramethoxysilane, tetra-n-propoxysilane, tetraisopropoxysilane,tetra-n-butoxysilane, tetraisobutoxysilane, phenyltriethoxysilane(PhTES), phenyltrimethoxysilane (PhTMS), diphenyldimethoxysilane,diphenyldiethoxysilane and the like.

As alkoxysilane having the above-mentioned polymerizable group, thereare given 3-methacryloxypropyltriethoxysilane (MPTES),3-methacryloxypropyltrimethoxysilane (MPTMS),3-methacryloxypropylmethyldimethoxysilane,3-acryloxypropyltrimethoxysilane, p-styryltriethoxysilane,p-styryltrimethoxysilane, vinyltrimethoxysilane, andvinyltriethoxysilane.

As the titanium alkoxide, there are given titanium isopropoxide,titanium butoxide and the like. As the zirconium alkoxide, there aregiven zirconium isopropoxide, zirconium butoxide and the like.

As the niobium alkoxide, there are given Niobium(V) ethoxide and thelike.

Though the above-mentioned substances can be used as the metal alkoxide,it is generally possible to use the metal alkoxides expressed byformulas, M(OR)_(n), R′M(OR)_(n-1) and R′₂M(OR)_(n-2), wherein Mrepresents metal, n is 2, 3, 4 or 5, and R and R′ represent an organicgroup. As the organic group, there are given an alkyl group, an arylgroup and organic groups having the above polymerizable groups. As themetal M, there are given Si, Ti, Zr, Al, Sn, Zn, Nb and the like asdescribed above. Further, as the alkyl group, an alkyl group having 1 to5 carbon atoms is preferred.

In the case where the organic-inorganic composite material is formedfrom the organic polymer and the metal alkoxide, the organic polymer isnot particularly limited as long as it can form the organic-inorganiccomposite material together with the metal alkoxide. As the organicpolymer, there can be given, for example, a high polymer having acarbonyl group, a high polymer having a benzene ring and a high polymerhaving a naphthalene ring.

As the specific example of the organic polymer, there can be given, forexample, polyvinyl pyrrolidone, polycarbonate, polymethyl methacrylate,polyamide, polyimide, polystyrene, polyethylene, polypropylene, epoxyresin, phenolic resin, acrylic resin, urea resin, melamine resin and thelike. Polyvinyl pyrrolidone, polycarbonate, polymethyl methacrylate,polystyrene, epoxy resin and the mixture thereof are preferably usedfrom the viewpoint of forming an organic-inorganic composite materialhaving high optical transparency.

When the organic-inorganic composite material is cured by light(ultraviolet) irradiation, it is preferred that the organic-inorganiccomposite material contains a photopolymerization initiator. Bycontaining the photopolymerization initiator, it can be cured by aslight quantity of light (ultraviolet) irradiation.

As a specific example of the photopolymerization initiator, there aregiven, for example, benzilketal, α-hydroxyacetophenone,α-aminoacetophenone, acylphosphine oxide, 1-hydroxy-cyclohexyl-phenylketone, 2-benzil-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1,trichloromethyltriazin, diphenyliodonium salt, triphenylsulfonium saltand imide sulfonate.

The core layer, the upper clad layer and the lower clad layer in thepresent invention-may be formed from an ultra violet (UV) curable resin.As such UV curable resin, there can be given, for example, epoxy UVcurable resins based on an epoxy resin, acrylic UV curable resins, epoxyacrylate UV curable resins, polyurethane UV curable resins and the like.

In accordance with the first aspect of the present invention, theoptical waveguide which can be easily fabricated and has a function of alens at an end portion can be made.

In accordance with the second aspect of the present invention, theoptical waveguide of which optical transmission characteristics can beeasily measured externally can be made.

In accordance with the third aspect of the present invention, theoptical waveguide, of which optical transmission characteristics can beeasily measured externally and which is easy to be aligned in beingconnected to another part, can be made.

In accordance with the fourth aspect of the present invention, athickness of a residual layer formed between an upper clad layer and alower clad layer around a core layer can be easily controlled.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing process steps of fabricating anoptical waveguide of an embodiment according to a first aspect of thepresent invention.

FIG. 2 is a perspective view showing a lower clad layer and a microlensin an optical waveguide of an embodiment according to the first aspectof the present invention.

FIG. 3 is a sectional side elevation view showing an optical waveguideof an embodiment according to the first aspect of the present invention.

FIG. 4 is a sectional side elevation view showing a conventional opticalwaveguide.

FIG. 5 is a sectional plan view showing an optical waveguide of anembodiment according to a second aspect of the present invention.

FIG. 6 is a sectional plan view showing an optical waveguide of anotherembodiment according to the second aspect of the present invention.

FIG. 7 is a sectional view showing fabrication steps of an embodimentaccording to the second aspect of the present invention.

FIG. 8 is a sectional view showing fabrication steps of an embodimentaccording to the second aspect of the present invention.

FIG. 9 is a sectional plan view showing an optical waveguide of anembodiment according to a third aspect of the present invention.

FIG. 10 is a sectional plan view showing an optical waveguide of anotherembodiment according to the third aspect of the present invention.

FIG. 11 is a longitudinal sectional view showing an optical waveguide ofanother embodiment according to the third aspect of the presentinvention.

FIG. 12 is a sectional view showing process steps of fabricating anoptical waveguide of an embodiment according to the third aspect of thepresent invention.

FIG. 13 is a sectional view showing process steps of fabricating anoptical waveguide of an embodiment according to the third aspect of thepresent invention.

FIG. 14 is a longitudinal sectional view showing an optical waveguide offurther another embodiment according to the third aspect of the presentinvention.

FIG. 15 is a plan view showing an optical waveguide of further anotherembodiment according to the third aspect of the present invention.

FIG. 16 is a plan view showing an optical waveguide of further anotherembodiment according to the third aspect of the present invention.

FIG. 17 is a plan view showing an optical waveguide of further anotherembodiment according to the third aspect of the present invention.

FIG. 18 is a sectional view showing fabrication steps of an embodimentaccording to the third aspect of the present invention.

FIG. 19 is a sectional view showing fabrication steps of an embodimentaccording to the third aspect of the present invention.

FIG. 20 is a sectional view showing an optical waveguide of anembodiment according to the fourth aspect of the present invention.

FIG. 21 is a plan view showing an optical waveguide of anotherembodiment according to the fourth aspect of the present invention.

FIG. 22 is a sectional view showing an optical waveguide of anotherembodiment according to the fourth aspect of the present invention.

FIG. 23 is a profile showing a state of distribution of effectiveindexes N_(eff) at a straight portion and a curved portion of a corelayer.

FIG. 24 is a plan view showing an optical waveguide of further anotherembodiment according to the fourth aspect of the present invention.

FIG. 25 is a view showing process steps of fabricating an opticalwaveguide of an embodiment according to the fourth aspect of the presentinvention.

FIG. 26 is a view showing process steps of fabricating an opticalwaveguide of an embodiment according to the fourth aspect of the presentinvention.

FIG. 27 is a sectional side elevation view showing an optical waveguideof another embodiment according to the first aspect of the presentinvention.

FIG. 28 is a perspective view showing a lower clad layer and a microlensin an optical waveguide of further another embodiment according to thefirst aspect of the present invention.

FIG. 29 is a perspective view showing a lower clad layer and a microlensin an optical waveguide of further another embodiment according to thefirst aspect of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described by way of examples,but the present invention is not limited to the following examples andcan be embodied by appropriately modifying within the scope of theclaims without changing the gist.

FIG. 1 is a sectional view showing process steps of fabricating anoptical waveguide of an embodiment according to a first aspect of thepresent invention. The optical waveguide of this embodiment has astructure shown in FIG. 1(e). That is, a lower clad layer 2 is providedon a substrate 1 and a core layer 3 extending along the longitudinaldirection of an optical waveguide is provided at the top central portionof the lower clad layer 2. The core layer 3 is provided in a groove 2 ain the lower clad layer 2. The groove 2 a has a rectangular crosssection. An upper clad layer 4 is provided on the core layer 3 and thelower clad layer 2. The lower clad layer 2 and the upper clad layer 4are formed from material having a lower refractive index than that ofthe core layer 3. The core layer 3 can transmit light through its insideby being shrouded in the upper clad layer 4 and the lower clad layer 2.

FIG. 1(e) shows a cross section of the vicinity of an end face of theoptical waveguide and a microlens 5 is located in the vicinity of an endface of the core layer 3 of the optical waveguide. In this embodiment,the microlens 5 has a substantially spherical shape. In this embodiment,the microlens 5 is formed from a spherical polystyrene particle.

Hereinafter, process steps of fabricating an optical waveguide shown inFIG. 1(e) will be described taken in conjunction with FIGS. 1(a)-1(d).In this embodiment and the following embodiments, the core layer, thelower clad layer and the upper clad layer are formed using anorganic-inorganic composite material formed from alkoxysilane. Thesolutions for forming a core layer and for forming a clad layer wereprepared as follows.

[Preparation of a solution for forming a core layer]

By mixing 5.5 ml of 3-methacryloxypropyltriethoxysilane, 5.5 ml ofphenyltriethoxysilane, 1.65 ml of hydrochloric acid (2N) and 20.5 ml ofethanol and leaving the mixture standing for 24 hours,3-methacryloxypropyltriethoxysilane and phenyltriethoxysilane arehydrolyzed and polycondensated. To 4 ml of the resulting polycondensate,10 ml of 1-hydroxy-cyclohexyl-phenyl ketone is added as a polymerizationinitiator, and then by heating to 100° C., ethanol is evaporated andremoved from the mixture to obtain viscous liquid. Into 1 g of thisviscous liquid, 3 ml of triethylethoxysilane and 0.8 ml oftrifluoroacetic anhydride are mixed and the mixture is left standing for24 hours, and then by heating the mixture to 100° C. to be dried,excessive triethylethoxysilane and trifluoroacetic anhydride areevaporated and removed from the mixture to obtain a solution for forminga core layer.

The refractive index of an organic-inorganic composite material formedfrom the solution for forming a core layer is 1.519.

[Preparation of a Solution for Forming a Clad Layer]

A solution for forming a clad layer is prepared by following the sameprocedure as described above except for using 5.5 ml of3-methacryloxypropyltriethoxysilane and 4.5 ml of phenyltriethoxysilanein preparation of a solution for forming a core layer described above.The refractive index of an organic-inorganic composite material formedfrom this solution is 1.515. An upper clad layer and a lower clad layerare formed using this solution.

[Fabricating of an Optical Waveguide]

As shown in FIG. 1(a), a solution 2 for forming a lower clad layer isadded dropwise onto a glass substrate 1, and then, as shown in FIG.1(b), a mold 6 having a projection portion 6 a is pressed against thelayer of the solution 2 for forming a lower clad layer and byirradiating ultraviolet light to the solution from the side of thesubstrate 1 in this state, the solution is cured to form a lower cladlayer 2 having a groove 2 a corresponding to the projection portion 6 a.The width and the height of the projection portion 6 a are 8 to 9 μm,respectively. Therefore, the width and the depth of the groove 2 aformed in the lower clad layer 2 are 8 to 9 μm, respectively. The mold 6is formed from resin or metal. The thickness of the lower clad layer 2is about 50 μm.

Next, a solution for forming a core layer is added dropwise onto aregion in the groove 2 a of the lower clad layer 2 other than thevicinity of an end face, and a solution for forming a core layercontaining a microlens is sucked up into a micropipet and this solutionis added dropwise together with the microlens particle from themicropipet to the groove 2 a of the vicinity of the end face in such away that the microlens particle is positioned in the vicinity of an endface of the groove 2 a while observing with a microscope. A standardparticle (“DYNOSPHERES SS-072-P” manufactured by JSR Corporation,spherical polystyrene particles, average particle diameter 7 to 8 μm,refractive index 1.586) is used as a microlens.

FIG. 1(c) shows a state of locating the microlens 5 in the vicinity ofan end face by following the procedure described above. Next, as shownin FIGS. 1(d), a flat plate 7 is pressed against on the lower clad layer2 and by irradiating ultraviolet light (365 nm) from the side of theglass substrate 1 with a load being applied, the solution for forming acore layer is cured to form a core layer 3.

Next, after the flat plate 7 is removed, a solution for forming an upperclad layer is added dropwise, and a flat plate is placed on this and aload is applied to this solution for several minutes to distribute thesolution uniformly over all, and then by irradiating ultraviolet light(365 nm) from the side of the glass substrate 1, the solution forforming an upper clad layer is cured to form an upper clad layer 4. Thethickness of the upper clad layer 4 is about 50 μm.

When a plurality of optical waveguides are simultaneously fabricatedfrom a single optical waveguide, after a upper clad layer is formed, anoptical waveguide is cut to the specified length through dicing and eachoptical waveguide is separated.

FIG. 2 is a perspective view showing the microlens 5 located in thevicinity of an end face of the lower clad layer 2 and the groove 2 a inthis embodiment. As shown in FIG. 2, in this embodiment, the microlens 5is located in the vicinity of an end face 10 of the optical waveguide.

FIG. 3 is a sectional side elevation view showing a vicinity of an endface of the optical waveguide of this embodiment. As shown in FIG. 3,the microlens 5 is located in the vicinity of an end face 10 of the corelayer 3 positioned between the lower clad layer 2 and the upper cladlayer 4. By thus locating the microlens 5 in the vicinity of the endface, it is possible to focus the waveguided light 8 transmitted throughthe optical waveguide 3 at the vicinity of the end face to make afocused light 9.

The microlens 5 is located in the core layer 3 around the end face 10and it is preferably located in such a way that a tip of the microlens 5is positioned in a region extending to a position distance equivalent toa radius of the microlens 5 from the end face 10. That is, when themicrolens 5 is located at the inner side of the optical waveguide, it ispreferably located in such a way that the tip, on the side of the endface 10, of the microlens 5 is positioned in a region of from theposition distance equivalent to a radius of the microlens 5 from the endface 10 to the end face 10. And, when the microlens 5 is located withthe lens's tip being projected out of the end face 10, it is preferablylocated in such a way that the tip of the microlens 5 is positioned in aregion of from the end face 10 to the position distance equivalent to aradius of the microlens 5 from the end face 10.

FIG. 4 is a sectional side elevation view showing an arrangement of aconventional microlens. Conventionally, as shown in FIG. 4, it isrequired to set up a microlens 40 outside the optical waveguide and ameans for securing the microlens 40 is required. And, alignment betweenthe microlens and the core required the accuracy on the order ofmicrometer. For this situation, in accordance with the first aspect ofthe present invention, since the microlens can be located within thecore layer, the microlens, it is possible to secure the microlens in thecore layer to integrate it into the core layer concurrently with theformation of the core layer. Further, alignment (alignment of an opticalaxis) between the microlens and the core can be unnecessary.

In the above embodiment, an article having a spherical shape has beenpresented as a microlens, but the microlens is not limited to such ashape in the first aspect. For example, an aspheric lens 14 may be usedas shown in FIG. 27. And, a lens that lens surface is cylindrical, acylindrical lens such as a rod lens and further a lens having a squareprism configuration may be used.

Further, as shown in FIG. 28, a spherical lens 15 having a cross sectionof ellipsoid, in which the major axis is vertical, may be used. In thiscase, in the groove 2 a of the clad layer 2, depth is longer than widthFurther, as shown in FIG. 29, a cylindrical lens 16 having a crosssection of ellipsoid may be used. In this case, depth is also longerthan width in a groove 2 a as with FIG. 28.

FIG. 5 is a sectional plan view showing an optical waveguide of anembodiment according to the second aspect of the present invention. Inthis embodiment, bubbles 20 are formed in the core layer 3. By formingbubbles 20 in the core layer 3, a light scattering region is formed. Awaveguided light 11 having passed through an end face 10 of the opticalwaveguide is scattered by particles in this light scattering region andpart of the scattered light is extracted out of the optical waveguide.

FIG. 6 is a sectional plan view showing a state of setting up aphotodetector 12 outside a region of the optical waveguide where thelight scattering region is formed. By setting up a photodetector 12outside a region of the optical waveguide where the light scatteringregion is formed, part of the waveguided light scattered by the lightscattering region can be detected. Therefore, in accordance with thesecond aspect of the present invention, light intensity of thewaveguided light transmitted through the core layer can be easilymeasured.

In this embodiment, the light scattering region is formed to be 1 mm inlength and the size of a bubble is 2 to 3 μm. And, the number of bubblesis about 20 to 30/mm³.

In the above embodiment, bubbles are formed in the core layer, butparticles may be contained in place of the bubbles. As such theparticles, there are given metal particles, glass particles and resinparticles.

FIGS. 7 and 8 are sectional views showing process steps of fabricatingan optical waveguide according to the second aspect of the presentinvention.

As shown in FIGS. 7(a) and 7(b), a lower clad layer 2 having a groove 2a for forming a core layer is formed on a substrate 1 and a solution 3for forming a core layer is added dropwise onto the lower clad layer 2to form a layer.

Next, as shown in FIG. 8(c), a solution for forming a core layercontaining bubbles is sucked up into a micropipet and this solution isinjected into a groove 2 a of a portion constituting the lightscattering region while observing with a microscope. The solution forforming a core layer containing bubbles is prepared by bubbling nitrogengas into the solution for forming a core layer through a porous filter(pore size 1 to 2 μm). Since the solution for forming a core layer is ahighly viscous solution, the bubbles injected into the groove 2 a remainin the groove 2 a. Incidentally, the width and the depth of the groove 2a are 6 to 7 μm, respectively. In addition, as described above, thelight scattering region formed by injecting bubbles has a length of 1mm, the size of a bubble is 2 to 3 μm and the number of bubbles is about20 to 30/mm³.

Next, as shown in FIGS. 8(d), a flat plate 7 is placed on the solution 3and the solution other than that in the groove 2 a is extruded byapplying a load 13. In this state, by irradiating ultraviolet light (365nm) from the side of the substrate 1 to the solution for forming a corelayer and curing it to form a core layer 3. As shown in FIGS. 8(d), theoptical waveguide becomes a state in which bubbles 20 are contained inonly the light scattering region.

Next, as shown in FIG. 8(e), after the flat plate 7 is removed, asolution for forming an upper clad layer is added dropwise and byirradiating ultraviolet light to this solution, the solution for formingan upper clad layer is cured to form an upper clad layer.

FIG. 9 is a sectional plan view showing an optical waveguide of anembodiment according to a third aspect of the present invention. In theembodiment shown in FIG. 9, a light scattering region 21, in whichbubbles 20 are contained, is formed in a region of part of the lowerclad layer 2. The light scattering region 21 is in a state that manybubbles 20 are formed in resin. Part of the waveguided light 11transmitting through the core layer 3 is leaked out of the core layer 3and scattered by the light scattering region 20, and part of thescattered light is extracted out of the optical waveguide. In theembodiment shown in FIG. 9, the core layer 3 has a curved portion andthe light scattering region 21 is formed outside the curved portion.Accordingly, since the light leaked from the curved portion can bescattered by the light scattering region 21 and detected by a sensor,set up externally, such as a photodiode, losses at the curved portioncan be measured.

FIG. 10 is a sectional plan view showing an optical waveguide of anotherembodiment according to the third aspect of the present invention. Inthis embodiment, a light scattering region 21 containing bubbles 20 isformed in the vicinity of an end face 10 of the optical waveguide. Anend face 30 a of an optical fiber 30 is connected to the end face 10 ofthe optical waveguide and a waveguided light 11 is transmitted from theoptical fiber 30 to the optical waveguide. In this embodiment, acoupling loss can be evaluated by scattering the emitted light generateddue to a loss of coupling to an optical fiber 30 in the light scatteringregion 21 and detecting the scattered light by a sensor, set up outsidethe optical waveguide, such as a photodiode.

As shown in FIG. 11, by forming the light scattering region 21 on bothsides of a core layer 3 and setting up a photodetector 12 which detectslight emitted from each light scattering region 21, it becomes possibleto align the core layer in connecting the optical waveguide to anoptical fiber, for example, by adjusting two photodetectors 12 in such away that two intensity of signals become identical to each other.

In FIGS. 10 and 11, light scattering region 21 may be formed, forexample, at a location 100 μm inwardly from the end face 10 and about 20μm apart from the core layer 3. The size of the light scattering regionmay be, for example, a region of the order of several mm cube. And abubble diameter is about 2 to 3 μm and the number of bubbles is about 20to 30 per 1 mm³ of the region.

FIGS. 12 and 13 are sectional views showing process steps of fabricatingan optical waveguide of an embodiment according to the third aspect ofthe present invention.

As shown in FIGS. 12(a) and 12(b), a solution 2 for forming a clad layeris added dropwise onto a substrate 1 to form a layer of a solution, andthe layer of the solution is irradiated with ultraviolet light from theside of the substrate 1 with a mold 6 having a projection portion 6 abeing pressed against the layer of the solution and cured to form a cladlayer 2 having a groove 2 a for forming a core layer.

Next, as shown in FIGS. 12(c), a solution 3 for forming a core layer isadded dropwise and a flat plate 7 is placed on this and by irradiatingultraviolet light from the side of the substrate 1, the solution in thegroove 2 a is cured to form a core layer 3.

Next, the flat plate 7 is removed as shown in FIG. 13(e), and a portion,where an light scattering region is to be formed, of the lower cladlayer is eliminated by dry etching technique to form two etchingportions 2 b on both sides of the core layer 3. Dry etching is carriedout in such a way that depth of etching is 5 to 10 μm after forming a Nimask (500 nm in thickness) on a region not to be etched by lift off.Conditions of dry etching are CF₄ gas flow rate: 10 sccm, degree ofvacuum: 25 mTorr, RF power: 200 W, and reactive ion etching (RIE) mode.After etching, Ni mask is removed with dilute hydrochloric acid andsample becomes a state shown in FIG. 13(e).

Next, as shown in FIG. 13(f), a solution for forming a clad layercontaining bubbles, which has been prepared in the same way as describedabove, is added dropwise onto the lower clad layer 2 and the etchingportion 2 b. After the solution placed on a region other than theetching portion 2 b is removed with a spatula, as shown in FIGS. 13(g),a flat plate 7 is placed on the solution and by irradiating ultravioletlight from the side of the substrate 1 with a load 13 being applied, thesolution for forming a clad layer is cured to form a light scatteringregion 21.

Next, after removing the flat plate 7, as shown in FIG. 13(h), an upperclad layer 4 is formed.

FIG. 14 is a longitudinal sectional view showing an optical waveguide offurther another embodiment according to the third aspect of the presentinvention. In this embodiment, a light scattering region 21 containingbubbles 20 is formed in an upper clad layer 4. After a solution forforming an upper clad layer is added dropwise, a solution for forming aclad layer, prepared in the same way as described above and containingbubbles 20, is added dropwise onto a peripheral portion where aprojection portion 31 a is positioned with a micropipet to allow thisportion to contain bubbles. Next, a mold 31 having the projectionportion 31 a is placed on the layer of the solution 4 for forming anupper clad layer, and bubbles 20 are concentrated in the vicinity of theprojection portion 31 a by applying a load. By irradiating ultravioletlight in this state and curing the solution, a light scattering region21, in which bubbles 20 are concentrated in the vicinity of a top of theupper clad layer, can be formed. After curing, the mold 31 is removed.Configuration of the projection portion 31 a of the mold 31 is, forexample, about 20 to 50 μm in width and length, respectively, and about20 μm in height. The mold 31 can be formed from, for example, resin ormetal.

FIG. 15 is a plan view showing an optical waveguide in which a lightscattering region 21 is formed above an upper clad layer 4 by a methodshown in FIG. 14. As shown in FIG. 15, by forming a light scatteringregion 21 on both side of the core layer 3 of the vicinity of an endface, a mark for a position of the end face of core layer in the opticalwaveguide is prepared. Therefore, when connecting the core layer to anoptical fiber, the light scattering region 21 can be employed as a markfor alignment.

FIG. 16 is a plan view showing an optical waveguide of further anotherembodiment according to the third aspect of the present invention. Inthis embodiment, a region other than the core layer 3 contains manybubbles 20 and a region other than the vicinity of the core layer 3 isadapted so as to be easily identified by the light scattering region.Since it becomes easy to identify a position of the core layer 3 in theoptical waveguide, assembling works such as coupling of optical fibersbecome easy.

FIG. 17 is a plan view showing an optical waveguide of further anotherembodiment according to the third aspect of the present invention. Inthis embodiment, bubbles 20 are concentrically formed in a region otherthan the core layer 3 and an light scattering region 21 is formed in arestricted region other than the core layer 3. Since bubbles 20 areconcentrated, bubble density becomes higher and the core layer 3 iseasier to identify than the embodiment shown in FIG. 16.

FIGS. 18 and 19 is a sectional view showing process steps of fabricatingan optical waveguide of an embodiment according to the third aspect ofthe present invention.

Process steps shown in FIGS. 18(a) to 18(d) are similar to that in FIGS.12(a) to 12(d) and a lower clad layer 2 is formed on a substrate 1 and acore layer 3 is formed in a groove 2 a in the lower clad layer 2.

Next, as shown in FIG. 19(e), in a portion where a light scatteringregion is to be formed, both sides of the lower clad layer 2 are dryetched and eliminated to form etching portions 2 c by dry etchingtechnique. Here, dry etching is carried out until the substrate 1 isexposed.

Next, as shown in FIG. 19(f), a solution for forming a clad layercontaining bubbles 20 is added dropwise with a micropipet, and as shownin FIGS. 19(g), a flat plate 7 is placed on the solution and in thisstate, ultraviolet light is irradiated from the side of the substrate 1to the solution and the solution is cured to form a light scatteringregion 21 containing bubbles 20.

Next, as shown in FIG. 19(h), an upper clad layer 4 is formed on thelower clad layer 2, the core layer 3 and the light scattering region 21.

FIG. 20 is a sectional view showing an optical waveguide of anembodiment according to the fourth aspect of the present invention.

As shown in FIG. 20, spacers 25 are located between the upper clad layer4 and the lower clad layer 2 around the core layer 3. By locating thespacers 25, the thickness of the residual layer 26 formed between theupper clad layer 4 and the lower clad layer 2 is controlled.

As a spacer used in the fourth aspect of the present invention, therecan be used a spacer for a liquid crystal display described above and astandard particle used in the first aspect of the present invention. Inthis embodiment, a fine silica particle (trade name “HIPRESICA”manufactured by UBENITTO Corporation, average particle diameter 0.2 μm,refractive index 1.35 to 1.45) is used. As a spacer 25, a spacer havinga lower refractive index is preferred. The leakage of light from theresidual layer 26 can be reduced by employing a spacer having a lowerrefractive index. In this embodiment, the refractive index of the corelayer 3 is 1.519, and the refractive indexes of the upper clad layer 4and the lower clad layer 2 are 1.515, respectively. Therefore, therefractive index of the spacer 25 is lower than that of the core layer3, the upper clad layer 4 and the lower clad layer 2.

In the fourth aspect of the present invention, the spacers 25 arepreferably provided in a region about 10 μm or more away from the corelayer 3. The reason for this is that optical transmissioncharacteristics in the core layer are not affected.

And, in accordance with the fourth aspect of the present invention, thethickness of the residual layer 26 can be controlled by locating thespacers 25 as described above. And, since the thickness of the residuallayer 26 is determined by the spacer 25, the uniformity of the thicknessof the residual layer in the substrate of the optical waveguide isimproved and also the reproducibility of the thickness of the residuallayer is improved. In the case of a single mode waveguide, since thewidth and the depth of the core layer 3 are about 5 to 8 μm, thethickness of the residual layer 26 is preferably controlled so as to be1.0 μm or smaller in the vicinity of the core layer 3. Further, in thecase of a multi mode waveguide, since the width and the depth of thecore layer 3 are about 50 μm, the thickness of the residual layer 26 ispreferably controlled so as to be 10 μm or smaller in the vicinity ofthe core layer 3.

FIG. 21 is a plan view showing further another embodiment according tothe fourth aspect of the present invention. In this embodiment, as shownin FIG. 21, the spacers 25 are located in only an inside region of thecurved portion of the core layer 3. FIG. 22 is a longitudinal sectionalview of a region where spacers are located. As shown in FIG. 22, in bothregions straddling the core layer 3, the spacers 25 are located in onlyone region. Therefore, the thickness of the residual layer 26 on theside where the spacers 25 are located is thickened and the thickness ofthe residual layer 26 on the opposite side is thinned.

As shown in FIG. 23(a), when a core layer 3 is straight, effectiveindexes N_(eff) on both sides of the core layer 3 are identical to eachother. As shown in FIG. 23(b), when a core layer 3 is curved, effectiveindex N_(eff) inside a curved portion becomes low but effective indexN_(eff) outside a curved portion becomes high. Therefore, leakage ofwaveguided light occurs at the outside of the curved portion and loss oflight is generated.

In this embodiment, the spacers are located in only an inside region ofthe curved portion to thicken the thickness of the residual layer 26inside the curved portion and to thin the thickness of the residuallayer 26 outside the curved portion. That is, the thickness of theresidual layer 26 is varied and graded so as to become thin in thedirection of from the inside to the outside of the curved portion.Therefore, as shown in FIG. 22, the effective index N_(eff) outside thecurved portion can be reduced. Accordingly, the loss of light generatedat the outside of the curved portion can be reduced.

As with the embodiments shown in FIGS. 21 and 22, in both sidesstraddling the core layer, when by locating spacers in only one side,the thickness of the residual layer is controlled so as to thin from oneside to the other side, the spaces are preferably located in a positionabout 50 μm away from the core layer. And, spacers used in this case maybe one having a relatively large size and therefore spacers used in aliquid crystal display are enough to be used. For example, spacers madefrom silica, having a particle diameter of 5 to 10 μm, can be used.

And, by providing spacers 25 in both sides straddling the core layer andchanging particle diameters of the spacers between both sides of thecore layer, the thickness of the residual layer may be controlled so asto be graded.

FIG. 24 is a plan view showing an optical waveguide of further anotherembodiment according to the fourth aspect of the present invention. Anoptical waveguide 42 is coupled to one end face 10 a of an opticalwaveguide 41. And, an optical waveguide 43 is coupled to the other endface 10 b of an optical waveguide 41. The width and the depth of thecore layer 3 of the optical waveguide 41 are 8 μm, respectively, and thewidth and the depth of the core layer 33 of the optical waveguide 42 are8 μm, respectively. On the other hand, the width and the depth of thecore layer 32 of the optical waveguide 43 are 9 μm, respectively, andthey are larger than that of the core layer 3.

In the optical waveguide 41, spacers 25 are located in both regionsstraddling the core layer 3 of the vicinity of the end face 10 b coupledto the optical waveguide 43. Therefore, the thickness of the residuallayer becomes thick in the vicinity of the end face 10 b. On the otherhand, spacers are not located in the vicinity of the end face 10 acoupled to the optical waveguide 42. Since the thickness of the residuallayer can be thickened by locating spacers 25 in a region of thevicinity of the end face 10 b, it is possible to widen a region of lightexiting the end face 10 b and to enhance a coupling property to the corelayer 32 which is more broad than that of the core layer 3.

In the embodiment shown in FIG. 24, the spaces 25 are preferablyprovided in a region about 50 μm away from the core layer 3 and thespaces 25 having a particle diameter of 5 to 10 μm are preferably used.

FIGS. 25 and 26 are sectional views showing process steps of fabricatingan optical waveguide of an embodiment illustrated in FIG. 20.

As shown in FIG. 25(a), a solution 2 for forming a lower clad layer isadded dropwise onto the substrate 1 and then a mold 6 having aprojection portion 6 a is placed on the solution 2 to apply a load 13,and in this state, ultraviolet light is irradiated from the side of thesubstrate 1. The width and the height of the projection portion 6 a are6 to 7 μm, respectively. As shown in FIG. 25(b), a lower clad layer 2having a groove 2 a for forming a core layer is formed, and as shown inFIG. 25(c), a solution 3 for forming a core layer is added dropwise ontothe lower clad layer 2.

After the unnecessary solution 3 for forming a core layer is removedwith a spatula or the like, as shown in FIGS. 25(d), a metal mask 34 isset up above a core layer 3. The metal mask 34 is a cover to preventspacers from adhering to regions of the order of 10 μm on both sides ofa core layer 3. Therefore, the metal mask 34 has a width of about 25 to30 μm. Next, spacers 25 are dropped in a dispersed state from above themetal mask 34 and spacers 25 adhere to regions, uncovered with the metalmask 34, on the lower clad layer 2.

Next, as shown in FIGS. 26(e), a flat plate 7 is placed on the spacers25 and by irradiating ultraviolet light from the side of the substrate 1with a load 13 being applied, a portion, in where the core layer 3 andthe spacers 25 are located, of the residual layer, is cured.

Next, after removing the flat plate 7, as shown in FIG. 26(f), an upperclad layer 4 is formed on the core layer 3 and the residual layer 26.

Also in the embodiment shown in FIGS. 21, 22 and 24, the respectivelayer can be fabricated by process steps similar to that described aboveusing a metal mask for locating spacers at only predetermined positionin each embodiment.

1. An optical waveguide comprising; a core layer to be an opticaltransmission region; and an upper clad layer and a lower clad layercovering said core layer; in which said core layer, said upper cladlayer and said lower clad layer are formed from resin materials; whereina microlens made of a material having a higher refractive index thanthat of a material constituting said core layer is disposed in thevicinity of an end face of said core layer.
 2. The optical waveguideaccording to claim 1, characterized in that said microlens has acurved-face partially in its outside shape.
 3. The optical waveguideaccording to claim 1, characterized in that said microlens has asubstantially spherical shape.
 4. The optical waveguide according toclaim 3, characterized in that said core layer is disposed in a grooveformed in said lower clad layer or said upper clad layer, and saidmicrolens is disposed in said groove in a state of being positioned bymeeting its outer surface with at least two inner wall surfaces of saidgroove.
 5. An optical waveguide comprising; a core layer to be anoptical transmission region; and an upper clad layer and a lower cladlayer covering said core layer; in which said core layer, said upperclad layer and said lower clad layer are formed from resin materials;characterized in that said optical waveguide is constructed in such away that a light guided in the core layer is scattered by a lightscattering region, which is formed by containing bubbles or particles ina part of said core layer, so that a part of the scattered light isextracted out of the optical waveguide.
 6. The optical waveguideaccording to claim 5, characterized in that a diameter of said bubble orparticle is at least a wavelength of the waveguided light.
 7. Theoptical waveguide according to claim 5, characterized in that saidbubbles are formed in said core layer by injecting a material forforming said core layer containing bubbles.
 8. An optical waveguidecomprising; a core layer to be an optical transmission region; and anupper clad layer and a lower clad layer covering said core layer; inwhich said core layer, said upper clad layer and said lower clad layerare formed from resin materials; characterized in that a lightscattering region containing bubbles or particles is formed in a part ofsaid upper clad layer and/or said lower clad layer.
 9. The opticalwaveguide according to claim 8, characterized by being constructed insuch a way that a part of emitted light in the clad layer can beextracted out of the optical waveguide by said light scattering region.10. The optical waveguide according to claim 8, characterized in thatsaid bubbles are formed in said clad layer by injecting a material forforming said clad layer containing bubbles.
 11. The optical waveguideaccording to claim 8, characterized in that said optical waveguide isformed by covering said upper clad layer and/or said lower clad layerwith a mold having a projection so as to concentrate bubbles around theprojection, when curing said upper clad layer and/or said lower cladlayer.
 12. An optical waveguide comprising; a core layer to be anoptical transmission region; and an upper clad layer and a lower cladlayer covering said core layer; in which said core layer, said upperclad layer and said lower clad layer are formed from resin materials;characterized in that spacers are disposed between said upper clad layerand said lower clad layer around said core layer.
 13. The opticalwaveguide according to claim 12, characterized in that said spacers aredisposed in only one region of both regions straggling said core layer.14. The optical waveguide according to claim 13, characterized in thatin a curved portion of said optical transmission region, said spacersare disposed only in an inside region of the curved portion.